Some climate scientists like to say "Climate is what you expect; weather is what you get". Weather is the day-to-day state of the atmosphere, based on quantifiable factors such as temperature, precipitation, atmospheric pressure, wind, sunshine, and cloud cover. Climate describes the long-term character of all weather variations, --the expected weather--, usually over a period of several years. The usual reference period is recent, when observations are more readily available and accurate.

Climate is most commonly thought of as the average value of these factors, but must also include their range and other measures of variability. For example, the long-term annual mean is seldom if ever matched by the mean for an individual year. The mean annual temperature at a marine and continental location may be similar, but the annual range of temperature near the ocean is relatively small.The ocean climate is a synthesis of conditions at a location within the ocean. Just as we have seasonal patterns of many factors on land, we have seasonal patterns of ocean factors such as temperature, currents and salinity. To know what is typical, we have to collect and analyze measurements of the ocean conditions for a number of years.

What Is Climate Change?

The climate at most locations is not steady or regular. There can be considerable variability in any factor. For example, temperature, precipitation, and ocean currents often differ from the mean state (the long-term average) or from the annual cycle. These variations occur on a variety of time scales, from year-to-year (e.g., El Niño and La Niña), decade-to-decade, (e.g., hydrologic and fisheries cycles), to centuries (e.g., ice ages). Factors that increase or decrease for an extended number of years may indicate a trend called 'Climate Change'. A similar trend that is widespread over of much of the earth may be a sign of Global Climate Change. Climate Changes are not always same-sign trends, or even linear (a constant rate of change over time).

Climate Change may also be seen as a shift in the frequency of El Niño events or changes in the annual cycle. Some of this Climate Change is due to natural factors, such as variability in solar activity, volcanic gases and dust in the atmosphere, or the distribution of heat in the ocean. However many scientists believe that anthropogenic (human-causes) factors have a considerable influence on changes in the Earth's climate observed over the past century. Global climate change is often commonly referred to as Global Warming, because of the apparent steady increase in global temperature over the past century. There are many complications to understanding the differences between Global Warming, Climate Change, and Greenhouse Gas Emissions related to the Earth's Climate.